INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Glass filled HDPE extrusion - much higher density than theoretical values.

Glass filled HDPE extrusion - much higher density than theoretical values.

Glass filled HDPE extrusion - much higher density than theoretical values.

(OP)
Hi all,

I am by no means a materials scientist or materials engineer so I hope that this is not a silly question.

We are reverse engineering our own product, as the material (a glass filled HDPE) was blended in another country by a company that wouldn't give us much by way of datasheets.

The (presumably E-glass) fill in the HDPE was measured by burnout test to be 25.6%. This is the average of 5 total tests with results ranging from 23.6% to 26.1%.

The density of the complete composite was measured by gas pycnometer to be 1.245g/cm3.

The density of the HDPE fraction therefore comes out, theoretically, at 1.056g/cm3.

To my knowledge, raw HDPE only gets up to around 0.98g/cm3. I have been told that residual compressive strain from extruding the product could cause the higher density, and thus it is not unexpected. But that would be a hell of a lot of strain (keeping in mind the poisson's ratio would not allow volume to drop in direct proportion to strain), and I could not find any reference to how large such an effect could be when I searched for it. Does that sound like a reasonable explanation, or is something more unexpected going on?

RE: Glass filled HDPE extrusion - much higher density than theoretical values.

I checked the numbers at my favorite density calculator:

http://www.netcomposites.com/calculators/volume-we...

You are right that something is off. If you need to deformulate this I may be able to help or send you to someone who can.

Chris DeArmitt PhD
President - Phantom Plastics LLC

Trusted adviser to leading companies around the world
www.phantomplastics.com

RE: Glass filled HDPE extrusion - much higher density than theoretical values.

(OP)
Yes, that is the same calc I did more or less. Personally I think the most likely reason for it is an error in the density reading.

Have you ever heard of HDPE showing significantly elevated densities under any conditions, e.g. internally compressively stressed and held there by the fiber fill? Could such an effect reasonably account for a roughly 10% higher density?

I have no real experience in the area of extrusions and composites, so I am not sure if this elevated density is an understood physical effect, or if something is simply wrong in either the measurements or the material.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close